1. Field of the Invention
This invention relates to a die machining apparatus in automatic programming which is applied when a die is machined from a work material by a machine tool, particularly a vertical type machining center.
2. Description of the Prior Art
Conventionally, when a work material as shown in FIG. 5 at A is machined to have the curved surface of a die such as is shown in FIG. 5 at B, in most cases, what is called a clamping cutting method has been applied. This is a method of setting a cutting depth and cutting a work several times by a vertical machining center using a ball end mill having a ball-shaped cutting edge.
The clamping cutting method is, however, inconvenient in the present state of the art. That is, since the length of the blade of the ball end mill is usually about 3 to 5 times the diameter of the ball, it is impossible to cut deeper than the length of the blade, and even when cutting to a depth which is less than the length of the blade, the available cutting force does not allow for cutting to a desired depth to be accomplished in one operation.
Therefore, several machining steps are required in order to obtain the final configuration of the curved surface of a die. For example, machining is conducted as is shown by models in FIG. 6a-6c in accordance with three steps from (C) to (E), thereby forming the traces of a tool, as is shown in (c).
The above-described method of machining in three steps, which is shown in FIGS. 6a-6c is disadvantageous in that the portion which is to be completed in conformity with a desired curved shape is subjected to repeated machining, which is a waste of time and means that the total machining time cannot be shortened.